The present invention relates generally to signal amplifiers and applications thereof. The accuracy of many electronic systems is degraded if amplifiers cannot supply currents that are sufficient to accurately amplify input signals. Several amplifier architectures have emerged, and amplifier designs can generally be designated according to an amplifier type or “class.” In portable applications, class D and class H amplifiers are often considered.
A Class D or “switching” amplifier is an electronic amplifier in which power devices, such as MOSFETs, are operated as switches. In a typical class D amplifier, the power devices are operated as binary on/off switches. Here, the switching mode of transistors is used to regulate power output. As a result, the class D amplifier achieves high power conversion efficiency. However, a drawback of the class D amplifier is high out-of-band noise and excess electromagnetic interference.
Other amplifier types, such as class H, rely upon auto-adjusted linear power rails. Class H amplifiers operate by continuously boosting and lowering the power supply, as required, above a certain minimum bias level. Although the efficiency of class H amplifiers is lower than class D, class H devices achieve lower out-of-band noise and better EMI characteristics. However, because its performance is too dependent upon its built-in supply rails, class H amplifiers are seldom selected to drive speakers in high performance audio systems and other applications.
Accordingly, the inventors have recognized a need for improved amplifier designs that can be used is many applications, such as audio systems and other portable applications. For example, the inventors have provided a configuration that combines the advantages of class D and class H amplifiers having efficiency higher than class H and out-of-band noise and EMI that is significantly improved compared to class D.